Rake receivers are well known. FIG. 1 illustrates an example 100 of one known rake receiver implementation. In the known rake receiver 100 separate rake filter modules 102, 112 are coupled to corresponding individual antennas 101, 103. Each filter module 102, 112 includes plurality of N fingers where each finger includes an individual delay element 104, 106, 114, 116 and a corresponding gain control element 108, 110, 118, 120. A first channel estimation and gain control module 105 is coupled to, and controls, the first rake filter module 102. A second channel estimation and gain control module 115 is coupled to, and controls, the second rake filter module 112. Each of the channel estimation and gain control modules 105, 115 perform a channel estimation operation for the channel corresponding to the individual antenna 101, 103 to which they are attached. As should be appreciated, a transmitted signal may follow multiple paths, e.g., due to reflections from buildings, etc., on its way to one of the antennas. Applying different delays and then combining the delayed signals can improve signal recovery by creating a composite signal from the delayed versions of the received signal. To achieve a coherent composite signal, each of the delayed versions of the received signal is subject to a different gain to reflect the signals contribution to the combined signal with the gain being a function of the estimated channel, e.g., with delayed signals more closely matching the main signal being weighted more heavily than delayed signal elements differing greatly from the main signal. The gains of the different delayed versions of the received signal are weighted according to the channel estimate generated by one of the separate channel estimation and gain control modules 105, 115.
In the illustrated system, the outputs of the individual rake fingers of module 102 are combined by a first summer 122 while the outputs of the rake fingers of rake filter module N 112, are combined by a second summer 124. The output of the two summers 122, 124 are then combined by a third summer 126 which is responsible for generating the combined signal produced from the output of antenna's 101, 103.
In the rake receiver 100, there are N rake fingers for each antenna 101, 103. In some cases, a single antenna 101, 103 may be the primary contributor to the combined output signal with the rake fingers coupled to the other antenna or antennas contributing little if anything to the combined output signal. However, in some cases, different fingers corresponding to different antennas may contribute significantly to the combined output signal. When fingers corresponding to different antennas are contributing significantly to the combined signal, often some fingers corresponding to one or both antennas will have very little contribution to the combined signal and may even have a gain set to zero reflecting their lack of useful contribution. Thus rake fingers which contribute little or not at all to the combined signal represent a potential waste of hardware resources.
It should be appreciated that the illustrated rake receiver 100 is hardware intensive in that each of the rake filter modules 102, 112 includes N rake fingers. In addition, two levels of signal summation are used to generate the output signal.
It would be desirable if methods and/or apparatus could be developed to reduce the hardware requirements for implementing rake receivers. In particular, it would be desirable if rake finger elements could be dynamically allocated and re-assigned to antennas to reduce total hardware requirements. In addition, it would be desirable if the rake fingers could be implemented in a flexible manner, e.g., with controllable delay and/or gain elements being included in one or more rake fingers.